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Neuromyelitis Optica (NMO)
Overview
- Neuromyelitis optica (NMO) characteristically involves bilateral optic neuritis with longitudinally extensive transverse myelitis.
Bilateral Optic Neuritis
- Unilateral optic neuritis is a key presenting symptom in MS but if optic neuritis is simultaneously bilateral or sequentially bilateral, we need to have a high index of suspicion for neuromyelitis optica (NMO).
Longitudinally Extensive Transverse Myelitis
- Transverse myelitis in NMO is longitudinally extensive.
- Indicate that it extends for greater than 3 levels but can potentially involve the entire length of the cord.
- As well, the myelitis in NMO is usually located centrally with a large cross-section; whereas, in MS, it’s commonly dorsolateral and the cross-sectional area is smaller.
- Thus, the clinical syndrome from the myelitis in NMO is clinically worse than in MS – it is more often complete and less likely to recover.
Area postrema
- NMO can characteristically attack the area postrema (in the dorsum of the medulla) and cause nausea and vomiting, as well as hiccups.
- This emetic center is particularly vulnerable because it has a large population of aquaporin-4 channel receptors.
Aquaporin-4 Antibodies
- IgG antibodies to the aquaporin-4 (AQP4) water channel are found in the majority of cases of NMO spectrum disorders (although, it’s important to note that NMO can also be AQP4-IgG negative) and is believed to have an important impact on its pathophysiology.
Female Predominance
- An important epidemiological distinguisher of NMO is that women are ~ 9 times more likely to suffer from NMO than men (in MS, this female:male ratio is closer to 3:1).
- As well, NMO is more common in people of nonwhite descent, including Asian, African, or Caribbean populations.
References
- See the Non-MS White Matter Disorders tutorial.